Fix implicit calculations with scalars and durations

Previously calculations where the scalar is first would be converted
to a duration of seconds but this causes issues with dates being
converted to times, e.g:

    Time.zone = "Beijing"           # => Asia/Shanghai
    date = Date.civil(2017, 5, 20)  # => Mon, 20 May 2017
    2 * 1.day                       # => 172800 seconds
    date + 2 * 1.day                # => Mon, 22 May 2017 00:00:00 CST +08:00

Now the `ActiveSupport::Duration::Scalar` calculation methods will try
to maintain the part structure of the duration where possible, e.g:

    Time.zone = "Beijing"           # => Asia/Shanghai
    date = Date.civil(2017, 5, 20)  # => Mon, 20 May 2017
    2 * 1.day                       # => 2 days
    date + 2 * 1.day                # => Mon, 22 May 2017

Fixes #29160, #28970.

1 files changed, 34 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/duration_test.rb b/activesupport/test/core_ext/duration_test.rb
index 1648a9b270..3108f24f21 100644
--- a/activesupport/test/core_ext/duration_test.rb
+++ b/activesupport/test/core_ext/duration_test.rb
@@ -337,6 +337,13 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal "no implicit conversion of String into ActiveSupport::Duration::Scalar", exception.message
   end
 
+  def test_scalar_plus_parts
+    scalar = ActiveSupport::Duration::Scalar.new(10)
+
+    assert_equal({ days: 1, seconds: 10 }, (scalar + 1.day).parts)
+    assert_equal({ days: -1, seconds: 10 }, (scalar + -1.day).parts)
+  end
+
   def test_scalar_minus
     scalar = ActiveSupport::Duration::Scalar.new(10)
 
@@ -349,6 +356,9 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal 5, scalar - 5.seconds
     assert_instance_of ActiveSupport::Duration, scalar - 5.seconds
 
+    assert_equal({ days: -1, seconds: 10 }, (scalar - 1.day).parts)
+    assert_equal({ days: 1, seconds: 10 }, (scalar - -1.day).parts)
+
     exception = assert_raises(TypeError) do
       scalar - "foo"
     end
@@ -356,6 +366,13 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal "no implicit conversion of String into ActiveSupport::Duration::Scalar", exception.message
   end
 
+  def test_scalar_minus_parts
+    scalar = ActiveSupport::Duration::Scalar.new(10)
+
+    assert_equal({ days: -1, seconds: 10 }, (scalar - 1.day).parts)
+    assert_equal({ days: 1, seconds: 10 }, (scalar - -1.day).parts)
+  end
+
   def test_scalar_multiply
     scalar = ActiveSupport::Duration::Scalar.new(5)
 
@@ -375,6 +392,14 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal "no implicit conversion of String into ActiveSupport::Duration::Scalar", exception.message
   end
 
+  def test_scalar_multiply_parts
+    scalar = ActiveSupport::Duration::Scalar.new(1)
+    assert_equal({ days: 2 }, (scalar * 2.days).parts)
+    assert_equal(172800, (scalar * 2.days).value)
+    assert_equal({ days: -2 }, (scalar * -2.days).parts)
+    assert_equal(-172800, (scalar * -2.days).value)
+  end
+
   def test_scalar_divide
     scalar = ActiveSupport::Duration::Scalar.new(10)
 
@@ -394,6 +419,15 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal "no implicit conversion of String into ActiveSupport::Duration::Scalar", exception.message
   end
 
+  def test_scalar_divide_parts
+    scalar = ActiveSupport::Duration::Scalar.new(10)
+
+    assert_equal({ days: 2 }, (scalar / 5.days).parts)
+    assert_equal(172800, (scalar / 5.days).value)
+    assert_equal({ days: -2 }, (scalar / -5.days).parts)
+    assert_equal(-172800, (scalar / -5.days).value)
+  end
+
   def test_twelve_months_equals_one_year
     assert_equal 12.months, 1.year
   end